1. Field of the Invention
A present invention relates to an image adjustment amount determination device, an image adjustment amount determination method and an image adjustment amount determination program for determining an image adjustment amount, and an image processing device that is constituted comprising the image adjustment amount determination device.
2. Related Background Art
‘Video’ is constituted by consecutive ‘frame images’ and each of the frame image is single still image. Video processing, which includes video capture, storage, transmission, display, encoding and decoding and so forth generally targets video for which the definition of the individual frame images (called simply ‘definition’ hereinbelow) is constant or changes gradually. However, the human eye is able to clearly distinguish differences in the definition of an image. Therefore, differences in definition are often directly linked to an evaluation of the quality of an image and, generally speaking, a high-definition image is evaluated as being of high quality.
Here, even when individual frame images are low-definition images (blurred images), in cases where the respective frame images are displayed as continuous video, an illusory phenomenon whereby this video is seen clearly by the person viewing the video as a video with improved definition of frame image and whereby the video is perceived as having smoother motion occurs is mentioned in ‘Takeuchi, T. & De Valois, K. K. (2005), “Sharpening image motion based on spatio-temporal characteristics of human vision”, Human Vision and Electronic Imaging X’ (called simply ‘Document 1’ hereinbelow). Such an illusory phenomenon is referred to as the ‘motion sharpening’ phenomenon (also referred to as the ‘motion-based definition phenomenon’).
The Document 1 mentions this motion sharpening phenomenon as probably being due to the magnitude of the motion of the photographed object contained in the frame images and the high frequency component of the spatial frequency. Furthermore, the Document 1 mentions that there are cases where, in the motion sharpening phenomenon, the definition of low-definition images is perceived as being higher than the actual definition when viewed as video as a result of frame images of a higher definition than a predetermined criterion (‘high-definition images’ hereinbelow) being inserted in video that is constituted by frame images of a lower definition than the predetermined criterion (called ‘low-definition images’ hereinbelow). In cases where 50% of the frame images constituting the video are constituted by high-definition images in particular, the definition perceived by the human eye viewing the video is sometimes seen as being no different from the definition when a video whose frame images are all constituted by high definition images is seen (that is, the illusion is that the definition that is perceived subjectively does not change). Thus, the motion sharpening phenomenon is also said to be a phenomenon whereby the subjective quality is maintained by mixing high-definition images and low-definition images.
Therefore, the present applicant considered whether this motion sharpening phenomenon was a type of masking phenomenon in a temporal direction that is also confirmed via a video scene change or the like. That is, high-definition images were thought to reduce (that is, mask) the difficulty in viewing low-definition images.
OOYAMA Tadasu, IMAI Shogo, WAKE Tenji, ‘Sensory Perception Psychology Handbook New Edition’ Seishin Shobo Co. Ltd, ISBN: 4414305039, Page 664' (called simply ‘Document 2’ hereinbelow) mentions the fact that the effects of masking phenomena generally change as a result of the relationship of the sizes of the spatial frequency components between mask simulation (simulation providing a masking effect) and target simulation (simulation receiving masking effect) and the display timing of the mask simulation and target simulation (Forward masking phenomenon and Backward masking phenomenon).
Furthermore, TAKEUCHI Tatsuto, ‘Motion-based video definition’, (Search date: Oct. 26, 2006), Internet <URL: http://www.ntt.co.jp/journal/0510/files/jn200510050.pdf> (called simply ‘Document 3’ hereinbelow) mentions the approach that the motion sharpening phenomenon is not a high-order visual perception mechanism such as memory or learning but rather a nonlinear motion of the mechanism that exists in the initial visual system of the human eye is brought about. Based on this fact, the present applicant considered the effect of both ‘motion’ between the frame images constituting the video and the ‘average luminance’ which has an extremely large influence on the initial visual system to be large in the motion sharpening phenomenon for which the subjective quality is preserved. Further, the ‘size of the spatial frequency component’ and the ‘temporal interval of the stimuli’ which determine the effect of the masking effect were also thought to be related to this phenomenon, and, in focusing on the characteristics of this video, the motion sharpening phenomenon was perceived to be a type of masking phenomenon.
However, in the Document 1 and the Document 3, the ‘size of motion’ and ‘constitution of the spatial frequency component’ are reported as feature quantities of video related to the motion sharpening phenomenon. However, the quantitative relationship between the feature quantities (the ‘size of motion’ and ‘constitution of the spatial frequency component’) and the effect of the motion sharpening phenomenon is not clear. Furthermore, with regard to the definition that is perceived in cases where the respective frame images are viewed as continuous video, in cases where the spatial frequency of the respective frame images is reduced (that is, the definition is reduced), although the results of experiments related to the degree of spatial frequency which the human eye is able to perceive have been reported, the conditions for preserving the definition perceived by the human eye (referred to as the ‘subjective definition’ hereinbelow) (that is, the conditions for preserving the subjective quality of video) have not been clarified.
Therefore, the present applicant arrived at the present invention because, when the relationship, in this motion sharpening phenomenon, between the feature quantity contained in the target video and the minimum spatial frequency component of low-definition images in which the subjective definition is preserved was calculated experimentally, it became clear that the minimum spatial frequency component of low-definition images in which the subjective definition is preserved differs depending on the relationship between the feature quantities of the low-definition images and high-definition images which are adjacent in their display order to the low-definition images.